The present invention relates to sensing elements or transducers for hydrophones, and more particularly to an integrating sensing element using piezoelectric polymer membranes.
Hydrophones are used to sense underwater acoustic signals or sounds for various purposes, as in sonar systems, for example, and may be deployed singly or in arrays of various configurations which may sometimes be at a substantial depth, depending on the particular purpose. The performance of a hydrophone, of course, depends on the sensitivity of the sensing elements which respond to the acoustic energy applied to the hydrophone, and there is a need for inexpensive sensing elements of small size with better sensitivity than those presently available and capable of withstanding relatively high hydrostatic pressures so that they can be used at considerable depths.
Prior attempts to improve the sensitivity of hydrophone sensing elements have been based on the approach of increasing the surface area of the face of the sensing element. This can be done by utilizing conventional ceramic materials for the sensing element, or by using piezoelectric polymer material configured in a conventional ceramic element design. The use of conventional ceramics in this way has not been successful because the maximum allowable surface area of a ceramic material is limited by the brittleness of ceramics and the difficulty of manufacturing ceramics in large sizes, while the ceramic is considerably more dense than sea water so that control of the hydrophone buoyancy becomes impractical for a large volume ceramic sensing element. The use of piezoelectric polymers in ceramic-type designs has also been unsuccessful because of unwanted coupling between various modes of vibration in the polymer, which prevents the development of the full potential advantage of such polymers.